This invention relates to a continuous extrusion method of manufacturing ceramic honeycomb structures with the aid of a screw type vacuum extruding machine, comprising continuously extruding a ceramic raw material batch through an extrusion die of the screw type vacuum extruding machine.
As a method of manufacturing ceramic honeycomb structures for use in catalyst supports for a device for purifying exhaust gases from internal combustion engines, various kinds of works, heat power plant and the like or from various kinds of chemical industries, etc., a method of extruding extrudable plastic raw material batches with the aid of a ram type extruding machine has heretofore been known.
But, such conventional method has drawbacks that the extrusion operation is intermittent and hence could not be effected in mass production scale, and that replacement of the batches for fresh batches and deairing step thereof are complex in operation. In addition, in order to obtain good extruded articles, the temperature of the extrudable raw material batch must be made substantially equal to the temperature of an extrusion cylinder to which is supplied the extrudable raw material batch. In practice, the heat conductivity of the extrudable raw material batch is different from that of the metallic extrusion cylinder. As a result, a slight temperature change causes an optimum extrusion condition to be degraded and hence there is a risk of the extruded articles being cracked and broken. Thus, it is extremely difficult to manufacture the extruded articles with a high yield.
On the one hand, in the ceramic field, it has been known that a continuous extrusion method which makes use of a screw type vacuum extruding machine is extremely excellent in its mass productivity. But, in the case of extruding structures such as a ceramic honeycomb structure composed of a thin-walled structure through an extrusion die having a small overall extrusion area and an extremely high extrusion resistance, it is required to use a very high extrusion pressure. As a result, between a screw of the screw type vacuum extruding machine and extrudable raw material batch is generated a high friction heat, so that the temperature of the extrudable raw material batches extruded by the screw becomes high at its center portion and that the temperature distribution in the extrudable raw material batch becomes non-uniform. As a result, it is impossible to obtain a uniform extrusion speed and hence there is a risk of the extruded article being cracked and broken. Thus, it has heretofore been almost impossible to manufacture a good article by the continuous extrusion method.